hypotl-ieee: Work around test failure on OSF/1 and native Windows.

hypotl-ieee: Work around test failure on OSF/1 and native Windows.

* m4/hypotl-ieee.m4: New file.
* m4/hypotl.m4 (gl_FUNC_HYPOTL): If gl_FUNC_HYPOTL_IEEE is present,
test whether hypotl works with mixed NaN and Infinity arguments.
Replace it if not.
* lib/math.in.h (hypotl): Override if REPLACE_HYPOTL is 1.
* m4/math_h.m4 (gl_MATH_H_DEFAULTS): Initialize REPLACE_HYPOTL.
* modules/math (Makefile.am): Substitute REPLACE_HYPOTL.
* modules/hypotl (configure.ac): Consider REPLACE_HYPOTL.
(Depends-on): Update conditions.
* modules/hypotl-ieee (Files): Add m4/hypotl-ieee.m4.
(Depends-on): Add hypot-ieee.
(configure.ac): Invoke gl_FUNC_HYPOTL_IEEE.
* doc/posix-functions/hypotl.texi: Mention the hypotl-ieee module.